Cain only seems better because he never had to face the same things yahwi did (im not saying he shouldve) but that's exactly what makes Yahwi an interesting character of growth.
The purpose of Cain's character is directed solely on Jooin and whatever past they shared (i still can't seem to make sense of this). Team Cain dwells well on this because they think relationships are meant to be all sunshine and rainbows when in reality it's not. Plus, this just means that Cain never had some sort of growth nor options to treat Jooin other than "gently".
On the other hand, with Yahwi's past, he had no way of understanding human relations beyond exhangeable exchanges and never even got to feel "love" till Jooin came along. People sticked to him for his reputation while Jooin was asking for love, something Yahwi was not acquainted with but also something that was already growing in him.
"Cain treats me better than you do" can you imagine how painful it was hearing that? Does anyone deserve to be compared? He tried to be better, and still no one saw his efforts. Imagine how difficult it can be for a human to repress himself for 20 years. And then, was judged when he fell into despair that caused his repressed emotions.
THE WHOLE PROBLEM HERE IS THAT THERE AINT NO COMMUNICATION GOING WELL FROM BOTH SIDES GOSH.

you probably just read my reply upside down